A hip joint socket is the part of a hip joint prothesis system that is to be implanted into the hip bone of a patient, while the other part, consisting of a shaft and a neck piece bearing a spherical head, represents the part of this system to be implanted into the femur.
Such a hip joint socket frequently comprises a socket support made of metal which can be inserted into the correspondingly prepared acetabulum bed and be mounted there, as well as an inner socket made of plastic that can be inserted in an interlocking manner into the concave side of the socket support, and the concave side of the inner socket serves as a bearing for the spherical head of the hip joint prothesis.
A prospectus of the PROTEK AG Company, CH-3001 Bern, 1988/1 edition and EPO 169978B1 disclose a full hip prothesis system CLS without cement. In this system, the socket support consists of a rotationally symmetrical hemispherical shell including six radial notches, which penetrate most of the hemispherical shell to form six tabs. The tabs become wider toward the equator and are arranged in the shape of a star. On these tabs are located outwardly directed anchoring points placed radially in three rows.
To implant this socket support into the prepared acetabulum bed the elastic tabs are pressed together with a collet chuck and the socket support is positioned in the acetabulum. When the collet chuck is released, the areas of the socket support near the equator are pressed against the bone by the tension acting radially outward. With an expansion cone or with a plastic inner socket, the socket support is then spread so that the anchoring points can be pressed into the bone and thus produce a stable primary anchoring of the socket support.
A secondary anchoring is made possible by the growth of bone substance on protrusions of the outer surface of the socket support, which are designed as firmly anchored fringes without undercut.
The elasticity of this socket support is present only to facilitate its insertion into the acetabulum With the collet chuck. To achieve this elasticity, moreover, the wall thickness in the transition area between the anchoring points and the pole is very thin. However, since the axis of symmetry of this implanted socket support is inclined at an angle of approximately 45.degree. to the axis of the patient's body, the forces transmitted from the spherical head of the joint prosthesis to the socket support in a patient who is standing are the greatest precisely where the socket support has its weakest places Thus, the danger exists that the socket support will become deformed, so that even under the normal stress of walking, for example, both the primary and the secondary anchoring can become loose. In any case, a solid connection to the bone may not be formed.
A further disadvantage is that this known socket support is both difficult and expensive to produce, particularly because of the numerous anchoring points which must be individually machined.